Even though a deal for Mata should be completed quickly, there is little chance of Chelsea immediately using the money to sign Barkley, who is out injured with a broken toe.

One short-term option for Chelsea is to relaunch a move for Inter Milan's Fredy Guarin, whose move to Juventus is yet to go through and who is available for £8m. The Colombian could provide cover for the rest of this season, particularly if Michael Essien is sold or loaned out.

PROCESS

But Chelsea's intention is to launch a big bid for midfielder Barkley in the summer and allowing Mata to go to United could aid that process.

Chelsea have the maximum number of non-homegrown over-21 players registered, 17, of which Mata is one. That is an issue the club will need to address, particularly with Frank Lampard, John Terry and Ashley Cole heading towards the end of their careers.

Jose Mourinho is hoping to sign Southampton's English left-back Luke Shaw as a long-term replacement for Cole, and may yet launch a bid in the final week of the transfer window. Barkley is also a major part of that strategy.

Everton want to secure him to a new contract and are expected to open talks with the 20-year-old in the near future, but there have been no detailed negotiations as yet and Barkley's current deal expires in 2016.

Chelsea have a close relationship with Everton, having sent striker Romelu Lukaku on loan to Goodison Park. Chairman Bruce Buck and technical director Michael Emenalo met Bill Kenwright, the Everton chairman, in London recently, although the exact reason for the high-powered get-together is not known.

What is clear is that Chelsea have earmarked Barkley as a key target and Mata's departure will free up cash and space in Mourinho's squad to try to get him. A deal for Mata may also rule David Moyes out of the running for Barkley, one of his former players, and leave Chelsea with just Manchester City as a competitor for his signature.

Barkley is understood to be happy at Everton and grateful to Roberto Martinez for giving him a regular first-team chance, but even if he signs a new deal before the end of the season, Everton may not be able to afford to turn down a lucrative offer and the player would be faced with a huge decision.

In recent years, Everton have been forced to sell Marouane Fellaini to United, Jack Rodwell and Joleon Lescott to City, Mikel Arteta to Arsenal and Steven Pienaar to Spurs. Wayne Rooney moved to United in 2004.